JP7463289B2 - Titanium dioxide particles - Google Patents

Description

The present invention relates to titanium dioxide particles and their production method, dispersions produced therefrom, and their use, particularly in personal care products.

Titanium dioxide has been used as an ultraviolet light attenuator in a wide range of applications including sunscreens, organic resins, films and coatings.

It is well known that both UVA and UVB radiation can play an important role in premature skin aging and skin cancer. Therefore, protection against both UVA and UVB radiation is very important to the end user. There is a continuing need to improve the balance of properties of inorganic, and especially titanium dioxide, sunscreens. This is especially true due to concerns over the toxicity of various organic UV (ultraviolet) absorbers, and the "yellowing" effect that certain organic UV absorbers have on inorganic sunscreens, which has led to an increased demand in recent years for "all inorganic" sunscreens.

Thus, there is a need for particulate titanium dioxide that exhibits high UVB absorption properties, yet also has effective UVA efficacy and improved transparency, particularly in non-nanoparticulate form, that can be used in a wide range of applications.

Surprisingly, we have discovered an improved titanium dioxide and method for its manufacture that overcomes or significantly reduces at least one of the problems discussed above.

Accordingly, the present invention provides titanium dioxide particles comprising: (i) a volume based median particle diameter D(v,0.5) greater than 175 nm; and (ii) an ( _E308 x _E360 )/ _E524 value greater than 300 l/g/cm.

The present invention also provides titanium dioxide particles having (i) an average crystal size of 30.0 to 51.0 nm, and/or (ii) an average aspect ratio of 1.05 to 1.55:1.

The present invention further provides titanium dioxide particles comprising: (i) an ( _E308 x _E360 )/ _E524 value of 320 l/g/cm or more; (ii) an _E524 of 7.5 l/g/cm or less; and optionally an _E308 x _E360 value of greater than 2100 (l/g/cm) ² .

The present invention also provides a dispersion comprising a dispersion medium and titanium dioxide particles as defined in the present disclosure.

The present invention further provides a sunscreen product comprising titanium dioxide particles and/or dispersions thereof as defined in the present disclosure.

The present invention further provides a method of producing titanium dioxide particles, comprising (i) forming precursor titanium dioxide particles having an average aspect ratio of 3.0 to 7.0:1, (ii) calcining the precursor particles to produce calcined titanium dioxide particles having an average crystal size of 30.0 to 51.0 nm and/or an average aspect ratio of 1.05 to 1.55:1, and optionally (iii) applying an inorganic and/or organic coating to the calcined titanium dioxide particles.

The present invention further provides a method of heating precursor titanium dioxide particles at a temperature above 400°C to produce calcined titanium dioxide particles, in which (i) the average width of the titanium dioxide particles is increased by 60-200%, and/or (ii) the BET specific surface area is decreased by 35-95%, and/or (iii) the average crystal size is increased by 200-400%.

The invention further provides titanium dioxide particles obtained by a process comprising: (i) forming precursor titanium dioxide particles having an average aspect ratio of from 3.0 to 7.0:1, (ii) calcining the precursor particles to produce calcined titanium dioxide particles, and optionally (iii) applying an inorganic and/or organic coating to the calcined titanium dioxide particles, the titanium dioxide particles having an _E524 of 7.5 l/g/cm or less and an ( _E308 x _E360 )/ _E524 value of 320 l/g/cm or more.

The present invention also provides the use of calcination to improve the UV absorption properties of titanium dioxide particles, wherein the calcined particles comprise an ( _E308 x _E360 )/ _E524 value of 320 l/g/cm or greater.

The titanium dioxide particles according to the invention preferably comprise anatase and/or rutile crystalline morphology. The titanium dioxide in the particles is suitably predominantly rutile, preferably more than 70% by weight, more preferably more than 80% by weight, particularly more than 90% by weight, especially more than 95% by weight, up to 100% by weight rutile.

The particles can be prepared by standard procedures, for example using the chloride process or by the sulfate process, or by hydrolysis of suitable titanium compounds, for example titanium oxydichloride or organic or inorganic titanates, or by oxidation, for example in the gas phase, of oxidizable titanium compounds.

In one embodiment, the titanium dioxide particles may be doped with a metal dopant selected from the group consisting of aluminum, chromium, cobalt, copper, gallium, iron, lead, manganese, nickel, silver, tin, vanadium, zinc, zirconium, and combinations thereof. The dopant is preferably selected from the group consisting of chromium, cobalt, copper, iron, manganese, nickel, silver, and vanadium, more preferably manganese and vanadium, especially manganese, especially in the 2+ and/or 3+ state.

Doping can be carried out by the usual methods known in the art. Doping is preferably obtained by co-precipitation of titanium dioxide and a soluble dopant complex, such as manganese chloride or manganese acetate. Alternatively, doping can be carried out by baking techniques by heating the titanium complex in the presence of a dopant complex, such as manganese nitrate, at a temperature above 500° C., usually below 1000° C. The dopant can be added by oxidizing a mixture containing the titanium complex and a dopant complex, such as manganese acetate, for example by spraying the mixture through a spray atomizer into an oxidation chamber.

The doped titanium dioxide particles preferably contain 0.01 to 3% by weight, more preferably 0.05 to 2% by weight, particularly 0.1 to 1% by weight, and especially 0.5 to 0.7% by weight of dopant metal, preferably manganese, based on the weight of titanium dioxide.

In one embodiment, initial or precursor titanium dioxide particles are prepared, for example, by hydrolysis of a titanium compound, in particular titanium oxydichloride, and these precursor particles are then subjected to a calcination process to obtain the titanium dioxide particles according to the invention.

The precursor titanium dioxide particles preferably have a rutile content as described above. Furthermore, the precursor titanium dioxide particles preferably contain less than 10% by weight, more preferably less than 5% by weight, especially less than 2% by weight, of amorphous titanium dioxide. The remaining titanium dioxide (i.e., 100% or less) is in crystalline form. In one embodiment, the titanium dioxide in the precursor particles is preferably substantially all in crystalline form.

The individual precursor titanium dioxide particles are preferably needle-like in shape and have a major axis (largest dimension or length) and a minor axis (smallest dimension or width). The third axis (or depth) of the particle is preferably about the same dimension as the width.

The number average length of the precursor titanium dioxide particles is suitably in the range of 40.0 to 85.0 nm, preferably 45.0 to 80.0 nm, more preferably 50.0 to 75.0 nm, especially 55.0 to 70.0 nm, and especially 60.0 to 65.0 nm. The number average width of the particles is suitably in the range of 8.0 to 22.0 nm, preferably 10.0 to 20.0 nm, more preferably 12.0 to 18.0 nm, especially 13.0 to 17.0 nm, and especially 14.0 to 16.0 nm. The precursor titanium dioxide particles suitably have an average aspect ratio _d1 : _d2 (where d1 and d2 are the length and width of the particle) in the range of 3.0 to 7.0:1, preferably 3.5 to 6.5:1, more preferably 4.0 to 6.0:1, especially 4.5 to 5.5: ₁ , and especially 4.8 to 5.2: ₁ . The dimensions of the precursor particles can be determined by measuring the length and width of several particles selected from photographic images obtained using a transmission electron microscope, as described in this disclosure.

The precursor titanium dioxide particles may suitably have an average crystal size (measured by X-ray diffraction as described herein) in the range of 6.0 to 15.0, preferably 7.0 to 13.5 nm, preferably 8.0 to 12.5 nm, more preferably 9.0 to 11.5 nm, particularly 9.5 to 10.5 nm, especially 9.8 to 10.2 nm.

The size distribution of the crystal size of the precursor titanium dioxide particles can be important and suitably at least 40%, preferably at least 50%, more preferably at least 60%, particularly at least 70%, especially at least 80% of the titanium dioxide particles have a crystal size within one or more of the above preferred ranges for the average crystal size.

The precursor titanium dioxide particles may have a BET specific surface area, measured as described in this disclosure, in the range of 75 to 140, suitably 80 to 125, preferably 87 to 115, more preferably 92 to 110, particularly 97 to 105, and especially 99 to 103 m ² g ⁻¹ .

The precursor titanium dioxide particles may have (i) an average pore size in the range of 40 to 115, suitably 50 to 105, preferably 60 to 95, more preferably 65 to 90, particularly 70 to 85, and especially 75 to 80 nm, measured by mercury porosimetry as described herein; and/or (ii) a total pore area in the range of 35 to 105, suitably 45 to 95, preferably 55 to 85, more preferably 63 to 80, particularly 68 to 77, and especially 71 to 74 m ² g ⁻¹ at 59,950.54 psia, measured by mercury porosimetry as described herein.

In one embodiment, the precursor titanium dioxide particles described herein are preferably calcined for less than 2 hours, more preferably from 2 minutes to 1.5 hours, particularly from 5 minutes to 1 hour, especially from 10 to 30 minutes. The precursor titanium dioxide particles may be calcined at a temperature above 400°C, suitably in the range of 450 to 900°C, preferably 500 to 850°C, more preferably 550 to 800°C, especially 600 to 750°C, especially 650 to 720°C.

For plant-scale production, e.g. amounts greater than 50 kg/hr, the precursor titanium dioxide particles are suitably calcined at a temperature in the range of 500-850°C, preferably 650-770°C, more preferably 690-730°C, particularly 700-720°C, especially 705-715°C.

In one embodiment, a continuous calcination process is used in which the precursor titanium dioxide particles are passed through a rotary calciner, which is preferably indirectly heated. The drum is preferably rotated while being heated, and the speed of the trommel determines the residence time of the titanium dioxide particles in the oven. The speed of the trommel is preferably in the range of 500-1,000 rpm, more preferably in the range of 600-900 rpm. The feed rate of the titanium dioxide particles to the oven can be suitably operated continuously by a screw conveyor, preferably in the range of 5-50% by weight, more preferably 10-40% by weight, especially 15-30% by weight, especially about 25% by weight of the total capacity of the screw conveyor. The feed rate of titanium dioxide to the oven is preferably in the range of 50-150 kg/h, more preferably 70-130 kg/h, especially 90-110 kg/h, especially 95-105 kg/h, for example for plant scale production.

In one embodiment, no pre-drying step is used and the precursor titanium dioxide particles subjected to the calcination process may contain water in the range of 40-75% by weight, preferably 50-70% by weight, more preferably 55-65% by weight, especially about 60% by weight, based on the total weight of the particles.

In another embodiment, a pre-drying step is used by heating the precursor titanium dioxide particles, preferably on a fluidized bed, at about 150°C for about 2 hours. The dried precursor titanium dioxide particles subjected to the calcination process preferably contain 1-15% by weight, more preferably 4-10% by weight, particularly 5-7% by weight, especially 5.5-6.5% by weight of water, based on the total weight of the particles.

The calcined titanium dioxide particles may have a BET specific surface area, measured as described herein, of at least 24 m ² g ^-1 , suitably in the range of from 24 to 42 m ² g ^-1 , more suitably from 27 to 39 m ² g ^-1 , preferably from 29 to 37 m ² g ^-1 , more preferably from 30 to 36 m ² g ^-1 , particularly from 31 to 35 m ² g ^-1 , and especially from 32 to 34 m ² g ^-1 .

In one embodiment, the calcination process described herein suitably results in a reduction in the BET surface area of the titanium dioxide particles (from precursor to calcined) of 35-95%, preferably 45-85%, preferably 55-80%, more preferably 60-75%, particularly 64-70%, and especially 66-68%, based on the BET surface area of the precursor particles.

The calcined titanium dioxide particles may have (i) an average pore diameter in the range of 75 to 160, suitably 85 to 150, preferably 95 to 140, more preferably 105 to 130, particularly 110 to 125, especially 115 to 120 nm, measured by mercury porosimetry as described herein; and/or (ii) a total pore area in the range of 20 to 53, suitably 24 to 48, preferably 28 to 44, more preferably 31 to 41, particularly 33 to 39, especially 35 to 37 m ² g ⁻¹ , measured by mercury porosimetry as described herein at 59,950.54 psia.

In one embodiment, the calcination process described herein results in (i) a reduction in the total pore area of the titanium dioxide particles (from precursor to calcined) at 59,950.54 psia, measured by mercury porosimetry as described herein, of 20 to 80%, preferably 30 to 70%, preferably 40 to 60%, more preferably 45 to 56%, particularly 48 to 53%, and especially 50 to 51%, based on the total pore area of the precursor particles at 59,950.54 psia; and/or (ii) an increase in the average pore size of the titanium dioxide particles (from precursor to calcined), measured by mercury porosimetry as described herein, of 10 to 90%, preferably 20 to 70%, preferably 30 to 55%, more preferably 35 to 47%, particularly 38 to 44%, and especially 40 to 42%, based on the average pore size of the precursor particles.

The calcined titanium dioxide particles suitably have an average aspect ratio d1:d2 (where d1 and d2 are the length and width of the particle respectively) in the range of from 1.05 to 1.55:1, preferably from _1.10 to 1.50:1, more preferably from 1.15 to _1.45 :1, particularly from 1.20 to 1.40: ₁ , and especially from 1.25 to 1.35: ₁ . The third axis (or depth) of the particle is preferably about the same dimension as the width.

The average length by number of the titanium dioxide particles is preferably in the range of 32.0 to 56.0 nm, preferably 37.0 to 51.0 nm, more preferably 40.0 to 48.0 nm, particularly 42.0 to 46.0 nm, and especially 43.0 to 45.0 nm. The average width by number of the particles is preferably in the range of 22.0 to 46.0 nm, preferably 27.0 to 41.0 nm, more preferably 30.0 to 38.0 nm, particularly 32.0 to 36.0 nm, and especially 33.0 to 35.0 nm. The size of the titanium dioxide particles can be determined by measuring the length and width of a plurality of particles selected from a photographic image obtained using a transmission electron microscope, as described in this disclosure.

In one embodiment, the calcination process described herein suitably results in an increase in the average width by number of titanium dioxide particles (from precursor to calcined) of in the range of 60-200%, preferably 80-180%, more preferably 95-160%, particularly 110-145%, and especially 120-135%, based on the average width by number of precursor particles.

The calcined titanium dioxide particles may have an average crystal size (measured by X-ray diffraction as described in this disclosure) in the range of 30.0 to 51.0 nm, suitably 34.0 to 51.0 nm, preferably 37.0 to 47.0 nm, more preferably 39.0 to 44.0 nm, particularly 41.0 to 44.0 nm, and especially 42.0 to 43.0 nm.

The size distribution of the crystal size of the calcined titanium dioxide particles can be important, and suitably at least 50%, preferably at least 60%, more preferably at least 70%, particularly at least 80%, and especially at least 90%, by weight of the titanium dioxide particles, have a crystal size within one or more of the above preferred ranges for the average crystal size.

In one embodiment, the calcination process described herein suitably results in an increase in the average crystal size of the titanium dioxide particles (from precursor to calcined) of between 200 and 400%, preferably between 235 and 375%, more preferably between 260 and 350%, particularly between 280 and 330%, and especially between 295 and 315%, based on the average crystal size of the precursor particles.

In one embodiment of the present invention, the titanium dioxide particles according to the invention, preferably the calcined particles, are coated with an inorganic and/or organic coating. The doped titanium dioxide particles may be uncoated, i.e., consist essentially of titanium dioxide and dopant.

In one embodiment, the inorganic coating is an oxide of aluminium, zirconium or silicon, or a mixture thereof, such as an alumina and silica mixture. The amount of inorganic coating, preferably alumina and/or silica, is suitably in the range of 1-12% by weight, preferably 2-6% by weight, more preferably 2.5-4.5% by weight, particularly 3-4% by weight, especially 3.3-3.7% by weight, based on the weight of the titanium dioxide core (or uncoated) particle.

In one embodiment of the present invention, the titanium dioxide particles are hydrophobic. The hydrophobicity of titanium dioxide can be determined by pressing a disk of titanium dioxide powder and measuring the contact angle of a drop of water placed thereon by standard techniques known in the art. The contact angle of hydrophobic titanium dioxide is preferably greater than 50°.

The titanium dioxide particles can be coated with a hydrophobizing agent to make them hydrophobic. Suitable coating materials are water repellent, preferably organic, and include fatty acids, preferably containing 10 to 20 carbon atoms, such as lauric acid, stearic acid and isostearic acid, salts of the above fatty acids, such as the sodium, potassium and/or aluminum salts of, fatty alcohols, such as stearyl alcohol, and silicones, such as polydimethylsiloxane and substituted polydimethylsiloxanes, as well as reactive silicones, such as methylhydrosiloxane and their polymers and copolymers. Stearic acid and/or its salts are particularly preferred.

In one embodiment, the titanium dioxide particles are treated with a fatty acid in the range of up to 15% by weight, suitably 1-10% by weight, preferably 2.5-7.5% by weight, more preferably 3.5-6% by weight, particularly 4-5.2% by weight, especially 4.4-4.8% by weight, based on the weight of the titanium dioxide core particle.

In one embodiment, the coating layer comprises a silane coupling agent, preferably an organosilane, more preferably a silane coupling agent represented by general formula (1).
_X4-n -Si-[ _Lm -Y] _n (1)
here,
Y is a functional group;
X is a hydrolyzable group;
L is a linking group;
m is 0 or 1, preferably 1;
n is 1 or 2, preferably 1.

Thus, preferred silane coupling agents are those represented by X ₃ -Si-LY. The at least one functional group (Y) can be selected, for example, from the group consisting of methyl, ethyl, vinyl, carboxyl, glycidoxy, epoxy, glycidyl, amino, mercapto, acryl and methacryl groups. The functional group preferably contains a nitrogen atom and is more preferably an amine group. The amine group may be a primary, secondary, tertiary or quaternary group, and is preferably a primary amine group.

Preferred amine groups are suitably represented by the formula _-NR2 , where each R is or includes a group selected from the group consisting of hydrogen, lower (i.e., C1-C6) alkyl, aryl, lower alkylaryl, lower arylalkyl, alkenyl, cycloalkenyl, alkene, alkylene, arylene, alkylarylene, arylalkylene, and cycloalkylene. In preferred embodiments, each R is independently selected from the group consisting of hydrogen and a straight chain or branched C1-C6 alkyl group, more preferably hydrogen and a C1-C4 alkyl group, and in particular both R groups are hydrogen.

At least one hydrolyzable group (X) can be -OR ¹ , -Cl, -Br, -I, and is preferably -OR ¹ , where each R ¹ is or comprises a radical selected from the group consisting of hydrogen, lower (i.e., C1-C6) alkyl, aryl, lower alkylaryl, lower arylalkyl, alkenyl, cycloalkenyl, alkene, alkylene, arylene, alkylarylene, arylalkylene, and cycloalkylene. Preferably, each R ¹ is independently selected from the group consisting of hydrogen and linear or branched C1-C6 alkyl groups, more preferably C1-C4 alkyl groups, especially C1-C2 alkyl groups, and especially ethyl groups.

The optional linking group (L) may comprise or consist of an alkyl, aryl, alkylaryl, arylalkyl, cycloalkyl, alkenyl, cycloalkenyl, alkene, alkenylene, cycloalkenylene, alkylene, arylene, alkylarylene, arylalkylene and/or cycloalkylene group. The linking group is preferably a linear or branched C1-C6 alkylene group, more preferably a C1-C4 alkylene group, especially a C3 alkylene, i.e. a propyl group.

Examples of suitable silane coupling agents include methyltrimethoxysilane, glycidoxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, phenyltrialkoxysilanes such as phenyltrialkoxysilane and diphenyldialkoxysilane, dialkyldialkoxysilanes such as dimethyldimethoxysilane and dimethyldiethoxysilane, quaternary silanes, and aminosilanes.

Aminosilanes are preferred and suitable materials include aminoethyltrimethoxysilane, aminoethyltriethoxysilane, aminopropyltrimethoxysilane, aminopropyltriethoxysilane, methylaminopropyltrimethoxysilane, ethylaminopropyltrimethoxysilane, aminopropyltripropoxysilane, aminoisobutyltrimethoxysilane and _{aminobutyltriethoxysilane} . A particularly preferred aminosilane is aminopropyltriethoxysilane ( _NH2 - _{CH2CH2CH2 - Si-} [ _OCH2CH3 ] ₃ ).

The amount of the silane coupling agent or its reaction product present in the coating layer is suitably up to 15% by weight, preferably 1 to 10% by weight, more preferably 3 to 7% by weight, particularly 3.5 to 5% by weight, especially 4 to 4.5% by weight, based on the weight of the titanium dioxide core particles.

The silane coupling agent is preferably used in the coating layer in combination with an inorganic material and/or a fatty acid (both as defined herein). The inorganic material is preferably silica, preferably amorphous and more preferably in a highly hydrated form, i.e. containing a high proportion of hydroxyl groups. The silica is preferably not in the form of high density silica. The fatty acid is preferably stearic acid and/or a salt thereof.

Suitably, the titanium dioxide core particles are coated with an inorganic material, preferably silica, dispersed in water, heated to a temperature in the range of 50-80°C, and then a silane coupling agent is added which reacts with the surface of the inorganic material and/or the surface of the titanium dioxide core particles. The fatty acid and/or its salt is preferably applied after the inorganic material and the silane coupling agent.

The titanium dioxide particles can be coated before or after the calcination step. In a preferred embodiment, the optional coating is applied to the particles after the optional calcination step. Thus, uncoated precursor titanium dioxide particles are preferably subjected to the calcination process described in this disclosure.

In one embodiment, the titanium dioxide particles are coated in situ during the formation of the dispersion according to the present invention. Such coatings can be applied by adding the coating material to the dispersion mixture prior to the milling process, as described in this disclosure. Examples of materials suitable for the in situ coating process are isostearic acid, oleth-3 phosphate, octyl/decyl phosphate, ceteth-5 phosphate, PPG-5-ceteth-10 phosphate, trideceth-5 phosphate, dobanol C12-C15 phosphate, C9-C15 alkyl phosphate, glyceryl triacetate, sorbitan laurate, sorbitan isostearate, sodium lauryl sulfate, sodium methyl cocoyl taurate, and mixtures thereof.

Titanium dioxide particles suitably coated according to the present invention may have a BET specific surface area, measured as described in this disclosure, in the range of 15 to 43 m ² g ^-1 , suitably 20 to 38 m ² g ^-1 , preferably 24 to 34 m ² g ^-1 , more preferably 26 to 32 m ² g ^-1 , especially 27 to 31 m ² g ^-1 , and especially 28 to 30 m ² g ^-1 . The BET specific surface area may be reduced by an amount in the range of 1.0 to 7.0 m ² g ^-1 , suitably 2.0 to 6.0 m ² g ^-1 , preferably 2.5 to 5.5 m ² g ^-1 , more preferably 3.0 to 5.0 m ² g ^-1 , especially 3.5 to 4.5 m ² g ^-1 , and especially 3.8 to 4.2 m ² g ^-1 when coating the preferably calcined titanium dioxide particles.

Suitably coated particles of titanium dioxide may have (i) an average pore diameter in the range of 65 to 150 nm, suitably 75 to 140 nm, preferably 85 to 130 nm, more preferably 95 to 120 nm, particularly 100 to 115 nm, especially 105 to 110 nm, measured by mercury porosimetry as described herein; and/or (ii) a total pore area at 59,950.54 psia in the range of 22 to 55 m ² g ⁻¹ , suitably 26 to 50 m ² g ⁻¹ , preferably 30 to 46 m ² g ⁻¹ , more preferably 33 to 43 m ² g ⁻¹ , especially 35 to 41 m ² g ⁻¹ , especially 37 to 39 m ² g ⁻¹ , measured by mercury porosimetry as described herein.

Suitably coated particles of titanium dioxide may have an average aspect ratio d1:d2 (d1 and d2 are the length and width of the particle respectively) in the range of from 1.05 to 1.55:1, preferably from _1.10 to 1.50:1, more preferably from 1.15 to 1.45: ₁ , particularly from _1.20 to 1.40: ₁ , and especially from 1.25 to 1.35:1. The third axis (or depth) of the particle is preferably about the same dimension as the width.

The average length by number of the titanium dioxide particles is preferably in the range of 32.0 to 56.0 nm, preferably 37.0 to 51.0 nm, more preferably 40.0 to 48.0 nm, particularly 42.0 to 46.0 nm, and especially 43.0 to 45.0 nm. The average width by number of the particles is preferably in the range of 22.0 to 46.0 nm, preferably 27.0 to 41.0 nm, more preferably 30.0 to 38.0 nm, particularly 32.0 to 36.0 nm, and especially 33.0 to 35.0 nm. The size of the titanium dioxide particles can be determined by measuring the length and width of a plurality of particles selected from a photographic image obtained using a transmission electron microscope, as described in this disclosure.

Suitably coated particles of titanium dioxide may have an average crystal size (as measured by X-ray diffraction as described in this disclosure) in the range of 30.0 to 51.0 nm, suitably 34.0 to 51.0 nm, preferably 37.0 to 47.0 nm, more preferably 39.0 to 44.0 nm, particularly 41.0 to 44.0 nm, especially 42.0 to 43.0 nm.

The size distribution of the crystal size of the titanium dioxide particles can be important, and suitably at least 50%, preferably at least 60%, more preferably at least 70%, particularly at least 80%, and especially at least 90% by weight of the titanium dioxide particles have a crystal size within one or more of the above preferred ranges for the average crystal size.

The size of suitably coated particles of titanium dioxide can be determined by measuring the length and width of several particles selected from a photographic image obtained using a transmission electron microscope, as described in this disclosure.

The titanium dioxide particles according to the invention can be in the form of a free-flowing powder. Powders having the required particle size can be produced by milling processes known in the art. The final milling stage of the titanium dioxide is suitably carried out in dry gas suspension conditions to reduce agglomeration. Fluid energy mills can be used where the agglomerated metal oxide powder is continuously injected into highly turbulent conditions in a closed chamber where multiple high energy collisions with the walls of the chamber and/or between the agglomerates occur. The milled powder is then conveyed to a cyclone and/or bag filter for recovery. The fluid used in the energy mill can be any cooled or heated gas or it can be superheated dry steam.

The titanium dioxide particles can be formed into a slurry, or preferably a liquid dispersion, in any suitable aqueous or organic liquid medium. By liquid it is meant liquid at ambient temperature (e.g., 25°C) and by dispersion it is meant a true dispersion, i.e., the solid particles are stable against agglomeration. The particles in a dispersion are relatively evenly distributed and are not prone to settling on standing, although if some settling does occur the particles can be easily redispersed by simple agitation.

Alternatively, the titanium dioxide particles can be in the form of a solid and/or semi-solid dispersion lotion or cream. Suitable solid or semi-solid dispersions can, for example, comprise in the range of 50-90% by weight, preferably 60-85% by weight, of titanium dioxide particles together with any one or more of the liquid media disclosed herein, or a high molecular weight polymeric material, such as a wax, e.g., glyceryl monostearate.

For use in sunscreen products, the liquid medium is preferably a cosmetically acceptable material. The liquid medium can be water or an organic medium, such as liquids such as vegetable oils, fatty acid glycerides, fatty acid esters and/or fatty alcohols. One suitable organic medium is a siloxane fluid, especially a cyclic oligomeric dialkylsiloxane, such as the cyclic pentamer of dimethylsiloxane, also known as cyclomethicone. Alternative fluids include dimethylsiloxane linear oligomers or polymers with suitable flow properties, and phenyltris(trimethylsiloxy)silane, also known as phenyltrimethicone.

Other suitable organic media include non-polar materials such as C13-C14 isoparaffin, isohexadecane, liquid paraffin (mineral oil), squalane, squalene, hydrogenated polyisobutene, and polydecene; and polar materials such as C12-C15 alkyl benzoates, caprylic/capric triglyceride, cetearyl isononanoate, ethylhexyl isostearate, ethylhexyl palmitate, isononyl isononanoate, isopropyl isostearate, isopropyl myristate, isostearyl isostearate, isostearyl neopentanoate, octyldodecanol, pentaerythrityl tetraisostearate, PPG-15 stearyl ether, triethylhexyl triglyceride, dicaprylyl carbonate, ethylhexyl stearate, sunflower (helianthus annus seed oil, isopropyl palmitate, and octyldodecyl neopentanoate, triethylhexanoin, ethylhexyl cocoate, propylene glycol isostearate, glyceryl isostearate, triisostearin, diethoxyethyl succinate, caprylyl eicoate, ethylhexyl hydroxystearate, lauryl lactate, butyl stearate, diisobutyl adipate, diisopropyl adipate, ethyl oleate, isocetyl stearate, propylene glycol dicaprylate/dicaprate, pentaerythrityl tetracaprylate/tetracaprate, oleyl oleate, propylene glycol isoceteth-3 acetate, PPG-3 benzyl ether myristate, cetearyl ethylhexanoate, ethylhexyl pelargonate, PPG-2 myristyl ether propionate, C14-C18 alkyl ethylhexanoate, and mixtures thereof.

In one embodiment, the organic medium is selected from the group consisting of isostearyl isostearate, isopropyl isostearate, triisostearin, ethyl oleate, dicaprylyl ether, and mixtures thereof.

In one embodiment, the organic medium is a vegetable oil, such as one selected from the group consisting of sweet almond oil, olive oil, avocado oil, grape seed oil, sunflower oil, meadowfoam seed oil, carrot oil, and mixtures thereof.

The dispersion according to the invention may also contain a dispersing agent to improve its properties. The dispersing agent is suitably present in the range of 1 to 30% by weight, preferably 4 to 20% by weight, more preferably 6 to 15% by weight, particularly 8 to 12% by weight, especially 9 to 11% by weight, based on the total weight of the titanium dioxide particles.

Suitable dispersants include substituted carboxylic acids, soap bases, and polyhydroxy acids. Typical dispersants can have the formula R.CO.AX, where A is a divalent atom, such as O, or a divalent bridging group. X can be hydrogen or a metal cation, or a primary, secondary, or tertiary amino group or their salts with acids, or a quaternary ammonium base. R can be the residue of a polyester chain, which, together with the -CO- group, is derived from a hydroxycarboxylic acid of the formula HO-R'-COOH. Examples of typical dispersants include those based on ricinoleic acid, hydroxystearic acid, and hydrogenated castor oil fatty acid, which contains, in addition to 12-hydroxystearic acid, small amounts of stearic acid and palmitic acid. Dispersants based on one or more polyesters or salts of hydroxycarboxylic acids and carboxylic acids without hydroxy groups can also be used. Compounds of various molecular weights can be used. Polyglyceryl-3 polyricinoleate and polyhydroxystearic acid are preferred dispersants. When the coating layer of the titanium dioxide particles includes a silane coupling agent as defined herein, polyglyceryl-3 polyricinoleate is particularly preferred. When the coating layer of the titanium dioxide particles does not include a silane coupling agent, polyhydroxystearic acid is particularly preferred.

Other suitable dispersants are monoesters of fatty acid alkanolamides and carboxylic acids and their salts. Suitable alkanolamides include, for example, those based on ethanolamine, propanolamine or aminoethylethanolamine. The dispersant can be one of what are commercially referred to as hyper dispersants. Polyhydroxystearic acid is a particularly preferred dispersant in organic media.

Suitable dispersants for use in aqueous media include polymeric acrylic acids or their salts. Partially or fully neutralized salts, such as alkali metal salts and ammonium salts, can be used. Examples of dispersants are polyacrylic acid, substituted acrylic acid polymers, acrylic acid copolymers, sodium and/or ammonium salts of polyacrylic acid, and sodium and/or ammonium salts of acrylic acid copolymers. Such dispersants are categorized as polyacrylic acid itself and its sodium or ammonium salts, and copolymers of acrylic acid with other suitable monomers, such as sulfonic acid derivatives, such as 2-acrylamido 2-methylpropanesulfonic acid. Comonomers polymerizable with acrylic acid or substituted acrylic acid can be those containing carboxyl groups. Typically, dispersants used in aqueous media have a molecular weight in the range of 1,000 to 10,000, and are preferably substantially linear molecules. Materials such as sodium citrate may be used as co-dispersants.

One advantage of the present invention is that it is possible to produce dispersions, especially liquids, which suitably contain at least 30% by weight, preferably at least 40% by weight, more preferably at least 45% by weight, particularly at least 50% by weight, especially at least 55% by weight, and typically up to 65% by weight, of titanium dioxide particles, based on the total weight of the dispersion.

In one embodiment, the preferably calcined titanium dioxide particles according to the invention in the dispersion have (i) a median particle size by volume (equivalent spherical diameter corresponding to 50% of the volume of all particles - often expressed as the "D(v,0.5)" value) of more than 175 nm, preferably more than 180 nm, more preferably more than 200 nm, even more preferably more than 220 nm, preferably more than 235 nm, more preferably more than 245 nm, particularly more than 255 nm, especially more than 265 nm, in the dispersion; and/or (ii) less than 360 nm, preferably less than 340 nm, more preferably less than 320 nm, preferably less than 305 nm, more preferably less than 295 nm, particularly less than 285 nm, especially less than 275 nm, in the dispersion; and/or (iii) any combination of (i) and (ii), measured as described herein.

In one embodiment, the suitably calcined titanium dioxide particles have a D(v,0.5) value greater than 175 nm, preferably in the range of 180 nm to 230 nm, more preferably 185 to 210 nm, particularly 190 to 200 nm, and especially 193 to 197 nm.

The size distribution of the titanium dioxide particles may also be an important parameter for obtaining the desired properties. In one embodiment, (i) less than 10% by volume of the titanium dioxide particles have a volume based diameter that is more than 50 nm, preferably more than 45 nm, more preferably more than 40 nm, preferably more than 35 nm, more preferably more than 32 nm, particularly more than 28 nm, and especially more than 25 nm smaller than the volume based median particle size; and/or (ii) less than 16% by volume of the titanium dioxide particles have a volume based diameter that is more than 45 nm, preferably more than 40 nm, more preferably more than 35 nm, preferably more than 30 nm, more preferably more than 25 nm, and especially more than 20 nm, and especially more than 18 nm smaller than the volume based median particle size; and/or (iii) more than 90% by volume of the titanium dioxide particles have a volume based diameter that is less than 140 nm, preferably less than 125 nm, more preferably less than 115 nm, and especially less than 105 nm smaller than the volume based median particle size. and/or (iv) more than 84% by volume of the titanium dioxide particles have a volumetric diameter that is less than 100 nm, preferably less than 85 nm, more preferably less than 75 nm, preferably less than 65 nm, more preferably less than 55 nm, particularly less than 45 nm, especially less than 40 nm, greater than the volumetric median particle size; and/or (v) any combination of (i), (ii), (iii) and/or (iv).

In one embodiment, the suitably calcined titanium dioxide particles according to the invention in the dispersion have (i) a diameter greater than 120 nm, preferably greater than 135 nm, more preferably greater than 145 nm, even more preferably greater than 155 nm, preferably greater than 165 nm, more preferably greater than 175 nm, particularly greater than 185 nm, especially greater than 195 nm; and/or (ii) less than 265 nm, preferably less than 255 nm, more preferably less than 245 nm, preferably less than 235 nm, more preferably less than 225 nm, particularly less than 215 nm, especially less than 205 nm; and/or (iii) any combination of (i) and (ii) a number based median particle diameter (equivalent spherical diameter corresponding to 50% of the number of all particles as read on a cumulative distribution curve for the diameter of the particles by volume percentage - often expressed as the "D(n,0.5)" value), measured as described herein.

In one embodiment, the suitably calcined titanium dioxide particles have a D(n,0.5) value of greater than 100 nm, preferably in the range of 110 nm to 175 nm, more preferably 120 to 155 nm, particularly 130 to 145 nm, and especially 135 to 140 nm.

In one embodiment, (i) less than 10% by number of the titanium dioxide particles have a number based diameter that is more than 50 nm, preferably more than 45 nm, more preferably more than 40 nm, preferably more than 35 nm, more preferably more than 32 nm, particularly more than 28 nm, and especially more than 25 nm, smaller than the number based median particle size; and/or (ii) less than 16% by number of the titanium dioxide particles have a number based diameter that is more than 45 nm, preferably more than 40 nm, more preferably more than 35 nm, preferably more than 30 nm, more preferably more than 25 nm, and especially more than 20 nm, smaller than the number based median particle size; and/or (iii) more than 90% by number of the titanium dioxide particles have a number based diameter that is less than 100 nm, preferably less than 85 nm, more preferably less than 70 nm, and especially less than 60 nm, smaller than the number based median particle size. and/or (iv) more than 84% of the titanium dioxide particles have a diameter by number that is less than 85 nm, preferably less than 70 nm, more preferably less than 55 nm, preferably less than 45 nm, more preferably less than 35 nm, particularly less than 30 nm, especially less than 25 nm, greater than the median particle size by number; and/or (v) any combination of (i), (ii), (iii) and/or (iv).

The size of the titanium dioxide particles in the dispersions according to the invention can be measured by techniques based on sedimentation analysis. The median particle size by volume can be determined by plotting a cumulative distribution curve representing the percentage of particle volume below a selected particle size and determining the 50th percentile. The median particle size by number can be determined by plotting a cumulative distribution curve representing the percentage of particle number below a selected particle size and determining the 50th percentile. The median particle volume and number diameters of the titanium dioxide particles and the particle size distribution can be suitably measured by forming a dispersion of titanium dioxide particles and using a Brookhaven particle size analyzer as described in this disclosure.

The size of titanium dioxide particles in a dispersion according to the invention can also be measured by a technique based on light scattering. The intensity of the scattered light is measured and a function is fitted to obtain the size using an algorithm that determines (i) a cumulant (or Z-average) average particle size, which gives one overall average particle size, and (ii) a peak size, which gives the average size based on the intensity of the scattered light. The intensity values can be converted to a number or volume distribution using Mie theory. This distribution represents the relative proportions of multiple components in a sample based on their mass or volume rather than their scattering (intensity) in the sample.

In one embodiment, the titanium dioxide particles in the dispersion have a Z-average particle size, measured by light scattering as described herein, of (i) greater than 80 nm, preferably greater than 100 nm, more preferably greater than 115 nm, preferably greater than 125 nm, more preferably greater than 130 nm, particularly greater than 135 nm, especially greater than 140 nm; and/or (ii) less than 230 nm, preferably less than 200 nm, more preferably less than 185 nm, even more preferably less than 170 nm, preferably less than 165 nm, more preferably less than 160 nm, particularly less than 155 nm, especially less than 150 nm; and/or (iii) any combination of (i) and (ii).

In one embodiment, the titanium dioxide particles in the dispersion have a Z-average particle size in the range of 135 to 230 nm, preferably 155 to 210 nm, more preferably 165 to 200 nm, particularly 175 to 190 nm, and especially 180 to 185 nm.

In one embodiment, the titanium dioxide particles in the dispersion have an intensity mean particle size, measured by light scattering as described herein, of (i) greater than 90 nm, preferably greater than 110 nm, more preferably greater than 125 nm, preferably greater than 135 nm, more preferably greater than 145 nm, particularly greater than 150 nm, especially greater than 155 nm; and/or (ii) equal to or less than 250 nm, preferably less than 220 nm, more preferably less than 200 nm, even more preferably less than 185 nm, preferably less than 175 nm, more preferably less than 170 nm, particularly less than 165 nm, especially less than 160 nm; and/or (iii) any combination of (i) and (ii).

In one embodiment, the titanium dioxide particles in the dispersion have an intensity average particle size in the range of 150 to 250 nm, preferably 175 to 230 nm, more preferably 185 to 220 nm, especially greater than 195 to 210 nm, especially 200 to 205 nm.

The titanium dioxide particles according to the present invention preferably exhibit improved transparency and may have (i) an extinction coefficient at 524 nm (E 524 ) of 7.5 l/g/cm or less, preferably 7.0 l/g/cm or less, preferably 6.8 l/g/cm or less, more preferably 6.6 l/g/cm or less, particularly 6.5 l/g/cm or less, especially 6.45 l/g/cm or less; and/or (ii) 4.7 l/g/cm or more, preferably 5.2 l/g/cm or more, more preferably 5.7 l/g/cm or more, preferably 6.0 l/g/cm or more, more preferably 6.2 l/g/cm or more, particularly 6.3 l/g/cm or more, especially 6.35 l/g/ _cm or more; and/or (iii) any combination of (i) and (ii), measured as described herein.

The titanium dioxide particles exhibit effective UV absorption, having (i) an extinction coefficient at 360 nm (E 360 ), measured as described herein, of greater than 20 l/g/cm, preferably greater than 27 l/g/cm, more preferably in the range of 32-50 l/g/cm, preferably 36-46 l/g/cm, more preferably 39-44 l/g/cm, particularly 40-43 l/g/cm, especially 41-42 l/g/cm; and/or (ii) an extinction coefficient at 308 nm (E ₃₀₈ ), measured as described herein, of greater than 45 l/g/cm, preferably greater than 50 l/g/cm, more preferably 55-76 l/g/cm, preferably 59-73 l/g/cm, more preferably 62-70 l/g/cm, particularly 64-68 l/g/cm, especially 65-67 l/g/ _cm. ); and/or (iii) any combination of (i) and (ii).

In one embodiment the titanium dioxide particles have (i) an E of less than 3500 (l/g/cm) ² , preferably 3300 (l/g/cm) ² or less, preferably 3150 (l/g/cm) ² or less, more preferably 2950 (l/g/cm) ² or less, particularly 2850 (l/g/cm) ² or less, especially 2800 (l/g/cm) ² or less; and/or (ii) an E of more than 1800 (l/g/cm) ² , preferably more than 2100 (l/g/cm) ² , more preferably 2300 (l/g/cm) ² or more, preferably 2450 (l/g/cm) ² or more, more preferably 2550 (l/g/cm) ² or more, particularly 2650 (l/g/cm) ² or more, especially 2700 (l/g/cm) ² or more; and/or (iii) any combination of (i) and (ii). ₃₀₈ x _E360 value.

In one embodiment, the titanium dioxide particles may have (i) an (E308 x E360)/E524 value of more than 300 l/g/cm, preferably at least 320 l/g/cm, more preferably at least 340 l/g/cm, preferably at least 365 l/g/cm, more preferably at least 385 l/g/cm, particularly at least 405, especially at least 425 l/g/cm; and/or (ii) less than 650 l/g/cm, preferably at most 570 l/g/cm, preferably at most 520 l/g/cm, more preferably at most ₄₈₅ l/g/cm, particularly at most 465 l/g/cm, especially at most ₄₄₅ l/g/cm; and/or (iii) any combination of (i) and ( _ii ).

In one embodiment, the titanium dioxide particles may have an E524 x E360 value of (i) less than 350 (l/g/cm) ² , suitably 320 (l/g/cm) ² or less, preferably 300 (l/g/cm) ² or less, more preferably 285 (l/g/cm) ² or less, particularly 275 (l/g/cm) ² or less, especially 270 (l/g/cm) ² or less; and/or (ii) greater than 190 (l/g/cm) ² , suitably 215 (l/g/cm) ² or more, preferably 230 (l/g/cm) ² or more, more preferably 245 (l/g/cm) ² or more, particularly 255 (l/g/cm) ² or more, especially ₂₆₀ (l _/ g/cm) ² or more; and/or (iii) any combination of (i) and (ii).

The titanium dioxide particles may have a λ(max) in the range of 290 to 355 nm, suitably 300 to 340 nm, preferably 308 to 330 nm, more preferably 313 to 324 nm, particularly 316 to 320 nm, and especially 317 to 319 nm, measured as described in this disclosure.

In one embodiment the titanium dioxide particles have (i) an E360/E524 ratio of greater than 5.0, suitably in the range of 5.5 to 8.0, preferably 5.9 to 7.3, more preferably 6.2 to 6.9, particularly 6.4 to 6.7, especially 6.5 to 6.6; and/or (ii) an _E308 / _E524 ratio of greater than 5.0, suitably in the range of 7.0 to 15.0, preferably 8.0 to 13.0, more preferably 9.0 to 12.0, particularly 9.5 to 11.5, especially 10.0 to 11.0; and/or (iii) an E360/E524 ratio x _E308 / _E524 ratio of greater than ₃₀ , suitably in the range of 40 to ₁₃₀ , preferably 50 to 100, more preferably 55 to ₈₅ , particularly 60 to 75, especially 65 to 70. ₅₂₄ ratio; and/or (iv) any combination of (i), (ii) and/or (iii).

The titanium dioxide particles may have an E ₃₆₀ /E ₃₀₈ ratio in the range from 0.30 to 0.90, suitably from 0.40 to 0.85, preferably from 0.45 to 0.80, more preferably from 0.50 to 0.75, especially from 0.55 to 0.70, and especially from 0.60 to 0.65.

The titanium dioxide particles, when present in a dispersion of, for example, 40% by weight, preferably exhibit a change in whiteness ΔL, measured as described in this disclosure, of less than 50, preferably in the range of 10 to 40, more preferably 20 to 36, particularly 27 to 33, and especially 29 to 31.

Compositions containing titanium dioxide particles according to the present invention, preferably end-use sunscreen products, preferably contain more than 0.5% by weight, more preferably in the range of 1-25% by weight, particularly 3-20% by weight, and especially 5-15% by weight, of the titanium dioxide particles described in the present disclosure, based on the total weight of the composition.

Such compositions according to the present invention preferably have (i) a Sun Protection Factor (SPF), measured as described herein, of greater than 10, preferably greater than 15, more preferably greater than 25, particularly preferably greater than 35, especially greater than 40, typically up to 60, and/or (ii) a UVA Protection Factor (UVAPF), measured as described herein, of greater than 6, preferably greater than 8, more preferably greater than 10, especially greater than 12, especially greater than 13, typically up to 20.

The composition suitably has a UVA/UVB ratio of less than 0.90, preferably in the range of 0.40 to 0.75, more preferably 0.50 to 0.70, particularly 0.60 to 0.66, especially 0.62 to 0.64.

The composition suitably has an SPF/UVAPF ratio of less than 8, preferably in the range of 1.5 to 3.5, more preferably 2.2 to 3.2, particularly 2.5 to 2.9, especially 2.6 to 2.8.

The critical wavelength of the composition is preferably greater than 360 nm, preferably in the range of 370 nm to 390 nm, more preferably 375 nm to 385 nm, particularly 377 nm to 381 nm, and especially 378 nm to 380 nm.

One surprising feature of the present invention is that the aforementioned SPF, UVAPF, and/or SPF/UVAPF ratio values are obtained when titanium dioxide as described herein is essentially the only UV attenuating agent present in the composition. By "essentially" we mean that any other inorganic and/or organic UV absorbers are present in an amount of less than 3% by weight, preferably less than 2% by weight, more preferably less than 1% by weight, particularly less than 0.5% by weight, and especially less than 0.1% by weight, based on the total weight of the composition.

The titanium dioxide particles preferably exhibit a change in whiteness ΔL of a sunscreen product containing the particles, measured as described in this disclosure, of less than 20, preferably in the range of 5 to 16, particularly 10 to 15, especially 13 to 14. The composition preferably has a ΔL/SPF ratio of less than 1, preferably in the range of 0.05 to 0.8, more preferably 0.2 to 0.6, especially 0.3 to 0.5, especially 0.35 to 0.45.

The titanium dioxide particles and dispersions of the present invention are useful as ingredients for preparing sunscreen compositions, particularly in the form of oil-in-water or water-in-oil emulsions. The compositions may further include conventional additives suitable for use in the intended application, such as conventional cosmetic ingredients used in sunscreens. As noted above, the particulate titanium dioxide defined in this disclosure may be the only UV attenuating agent present, however, other sunscreen agents may be added, such as other titanium dioxide, zinc oxide and/or other organic UV absorbers. For example, the titanium dioxide particles defined in this disclosure may be used in combination with other existing commercially available titanium dioxide and/or zinc oxide sunscreens.

The titanium dioxide particles and dispersions of the present invention can be used in combination with organic UV absorbers, such as butyl methoxydibenzoylmethane (avobenzone), benzophenone-3 (oxybenzone), 4-methylbenzylidene camphor (enzacamene), benzophenone-4 (sulisobenzone), bisethylhexyloxyphenol methoxyphenyl triazine (bemotrizinol), diethylamino hydroxybenzoyl hexyl benzoate, diethylhexyl butamido triazone, disodium phenyl dibenzimidazole tetrasulfonate, drometrizole trisiloxane, ethylhexyl dimethyl PABA (padimate O ), ethylhexyl methoxycinnamate (octinoxate), ethylhexyl salicylate (octisalate), ethylhexyl triazone, homosalate, isoamyl p-methoxycinnamate (amyloxate), isopropyl methoxycinnamate, methyl anthranilate (merazimate), methylene bis-benzotriazolyl tetramethylbutylphenol (bisoctrizole), octocrylene, PABA (aminobenzoic acid), phenylbenzimidazole sulfonic acid (ensulizole), terephthalidene dicamphor sulfonic acid, and mixtures thereof.

The following test methods were used in this specification:

1) Particle size measurement of titanium dioxide particles A small amount of titanium dioxide powder (typically 2 mg) was pressed into approximately 2 drops of ultrapure water (ELGA Medica R7) using the tip of a steel spatula for 1-2 minutes. The resulting suspension was diluted with water and shaken vigorously. Samples were mounted on carbon-coated grids suitable for transmission electron microscopy and air-dried before loading into a JOEL 2100F PE6-TEM. Images were taken at appropriate precise magnification using an accelerating voltage of 200 kV. Approximately 300-500 particles were displayed at approximately 2 diameter intervals. A transparent size grid consisting of a row of circles of gradually increasing diameter, representing spherical crystals of equal volume, was used to determine the size of a minimum number of 300 particles. Under each circle, a series of ellipsoids was outlined, representing spheroids of equal volume with gradually increasing eccentricity. The basic method assumes a log normal distribution with a standard deviation in the range of 1.2 to 1.6 (a wider particle size distribution would require more particles to be counted, e.g., on the order of 1000). The suspension method described above is suitable for producing nearly perfectly separated titanium dioxide particles while introducing minimal crystal breakage. Residual aggregates are sufficiently well defined that they and small debris can be ignored, and in effect only individual particles are included in the count. The average length, average width, average aspect ratio, and size distribution of the titanium dioxide particles were calculated from the measurements described above.

2) Crystal Size Measurement of Titanium Dioxide Particles Crystal size was measured by X-ray diffraction (XRD) line broadening. Diffraction patterns were measured using a Bruker D8 diffractometer equipped with an energy dispersive detector acting as a monochromator. The power of the X-ray generator was set at 40 kV and 40 mA. Diffraction was measured using a programmable slit of 0.6 mm with a step size of 0.05°. The data was analyzed by fitting the diffraction pattern between 2θ 22° and 48° to a series of peaks corresponding to the positions of rutile reflections and an additional series of peaks corresponding to the reflections of anatase, if present. The fitting process allowed the effect of instrumental broadening on the shape of the diffraction lines to be removed. The value of the average crystal size was determined based on the full width at half maximum (FWHM) for the rutile 110 reflection (2θ approximately 27°) using the Scherrer equation described in BE Warren, “X-Ray Diffraction”, Addison-Wesley, Reading, Massachusetts, 1969, pp 251-254.

3) Particle Median Size and Particle Size Distribution of Titanium Dioxide Particles in Dispersion i) An organic liquid dispersion of titanium dioxide particles was made by mixing 5 g of polyhydroxystearic acid (or polyglyceryl-3 polyricinoleate if a silane coupling agent was present in the coating layer) with 45 g of C12-C15 alkyl benzoate and then adding 50 g of titanium dioxide powder to the mixture. The mixture was passed through a horizontal bead mill operating at 4,500 rpm containing zirconia beads as the grinding media for 60 minutes.
(a) A dispersion of titanium dioxide particles was diluted to 15-25 g/L by mixing with isopropyl myristate. The diluted samples were analyzed with a Brookhaven BI-XDC Particle Sizer in centrifuge mode to measure the median diameter and particle size distribution based on volume and number. Measurements were performed at a speed of 1,000 rpm and particle size was determined based on the time it took for the particles to settle in the detector according to Stokes' law (determined using X-ray light). And/or (b) A dispersion of titanium dioxide particles was diluted to 1-10 g/L by mixing with a solution of C12-C15 alkyl benzoate containing 3% by weight polyhydroxystearic acid. The diluted samples were transferred to disposable plastic cuvettes and analyzed with a Malvern Zetasizer Nano ZS. The instrument starts by first measuring the equilibrium phase, then analyzes the scattered light intensity from the sample and determines the hydrodynamic volume of the particles based on Brownian motion in the suspension. Cumulant average (Z-average) values were calculated by the cumulant method described, for example, in Koppel, DE “Analysis of Macromolecular Polydispersity in Intensity Correlation Spectroscopy: The Method of Cumulants” J. Chem. Phys 57 (11), pp 4814-4820, 1972. Intensity-based average diameter, number-based average diameter, and volume (mass)-based average diameter were also determined.

ii) An aqueous dispersion was prepared by mixing 6.2 g of polyglyceryl-2 caprate, 2.6 g of sucrose stearate, 2 g of jojoba oil, 0.6 g of squalane, 1 g of caprylyl caprylate, and 37.4 g of deionized water, then adding 50 g of titanium dioxide powder to the mixture. The mixture was passed through a horizontal bead mill operating at 4,500 rpm containing zirconia beads as the grinding media for 60 minutes.
(a) A dispersion of titanium dioxide particles was diluted to 15-25 g/L by mixing with a 0.1% by weight aqueous solution of Isodeceth-6. The diluted sample was analyzed in a Brookhaven BI-XDC Particle Sizer in centrifuge mode and the volumetric median diameter, numbertric median diameter and particle size distribution were measured as described above for the organic dispersions. and/or (b) A dispersion of titanium dioxide particles was diluted to 1-10 g/L by mixing with deionized water. The diluted sample was transferred to a disposable plastic cuvette and analyzed with a Malvern Zetasizer Nano ZS. The instrument begins by first measuring the equilibrium phase, then analyzes the scattered light intensity from the sample and determines the hydrodynamic volume of the particles based on Brownian motion in the suspension. The cumulant mean (Z-average) value, intensity-based mean diameter, number-based mean diameter and volumetric (mass) mean diameter were measured as described above for the organic dispersions.

4) BET specific surface area of titanium dioxide particles
BET specific surface area was measured using a Micromeritics Gemini VII2390P. 0.4-0.5 g of dried titanium dioxide powder was introduced into a sample tube and degassed under nitrogen at room temperature for 10 minutes, then heated to 200°C and held at this temperature for 3 hours and again held under nitrogen. The dried sample was immersed in liquid nitrogen (-196°C) and once the sample was frozen, the specific surface area (SSA) was analyzed using nitrogen.

5) Mercury porosimetry pore size of titanium dioxide particles
Pore size distribution was measured using a Micromeritics Autopore V porosimeter. Approximately 0.1 g of dry titanium dioxide powder was weighed into the penetrometer bulb. The penetrometer containing titanium dioxide was loaded into the Micromeritics Autopore V porosimeter and measurements were made from 0.33 to 60,000 psia during intrusion and extrusion cycles. The average pore size and total pore area at 59,950.54 psia were determined.

6) Change in Whiteness of Titanium Dioxide Particles i) An organic or aqueous titanium dioxide dispersion (e.g., as described in 3) above) was coated onto the surface of a glossy black card and drawn down using a No. 2 K bar to form a film with a wet thickness of 12 microns. The film was allowed to dry at room temperature for 10 minutes and the whiteness of the coating on the black surface (L _F ) was measured using a Minolta CR300 colorimeter. The change in whiteness, ΔL, was calculated by subtracting the whiteness of the substrate (L _S ) from the whiteness of the coating (L _F ).
ii) A sunscreen formulation (e.g., as described in Example 3) was coated onto the surface of a glossy black card and drawn down using a No. 2 K bar to form a film with a wet thickness of 12 microns. The film was allowed to dry at room temperature for 10 minutes and the whiteness of the coating on the black surface (L _F ) was measured using a Minolta CR300 colorimeter. The change in whiteness, ΔL, was calculated by subtracting the whiteness of the substrate (L _S ) from the whiteness of the coating (L _F ).

7) Sun Protection Factor and UVA/UVB Ratio The sun protection factor (SPF) of sunscreen formulations (e.g. as described in Example 3) was determined using the in vitro method of Diffey and Robson, J. Soc. Cosmet. Chem. Vol. 40, pp 127-133, 1989. This method was also used to determine the UVA/UVB ratio of sunscreen formulations, which is determined by analyzing the area under the absorption curve related to the UVB part of the curve divided by the area related to the UVA part of the curve.

8) UVA Protection Factor and Critical Wavelength The UVA protection factors (UVAPF ₀ and UVAPF) of sunscreen formulations (e.g. as described in Example 3) were determined as described in the COLIPA guideline "Method for In Vitro Determination of UVA Protection Provided by Sunscreen Products Edition of 2011". A Labsphere UV-2000S UV Transmittance Analyzer was used. Using this method, the critical wavelength of the formulation was also determined, which indicates the wavelength at which 90% of the area under the absorbance curve lies.

A blank (100% transmission) sample was made by spreading 1.30 mg cm ^-2 (equivalent to 0.0325 g) of glycerin onto the rough surface of a polymethyl methacrylate (PMMA) plate (Helioplates HD6 from Laboratoire Helios Science Cosmetique). The sunscreen formulation was applied to the rough surface of the same PMMA plate at a concentration of 1.30 mg cm ^-2 (equivalent to 0.0325 g) as a series of small dots distributed evenly across the surface of the plate. Immediately after application, the formulation was spread across the surface of the plate using a latex-gloved finger. The coated plates were allowed to dry in the dark for 15 minutes. Immediately after drying, a total of nine UV transmission spectra (290-400 nm) were recorded for each plate at different positions. Three different plates were used to obtain an average of 27 readings of UV transmission data at each wavelength. The UV light transmitted through the coated plates was quantified at every 1 nm increment. The individual transmittance measurements obtained at each wavelength increment were used to calculate an initial UVA protection factor (UVAPF ₀ ). Plates treated with the same sunscreen formulations were then subjected to a simulated sunlight exposure using a long-arc xenon Atlas Suntest CPS+ insolator with a single UV dose calculated by the instrument and related to UVAPF ₀ , after which a second series of transmission measurements were made through the samples. The same number of measurements (i.e. 9 x 3 plates) were made prior to the simulated sunlight exposure. Again, the transmittance values were converted to absorbance values and the UVA protection factor (UVAPF) after exposure was calculated.

9) Extinction Coefficient i) A 0.1 g sample of an organic liquid titanium dioxide dispersion (e.g., as described in 3) above) was diluted with 100 ml of cyclohexane. The diluted sample was then further diluted with cyclohexane in a sample:cyclohexane ratio of 1:19. The total dilution ratio was 1:20,000.
ii) A 0.1 g sample of an aqueous titanium dioxide dispersion (e.g., as described in 3) above) was diluted with 100 ml of deionized water. The diluted sample was then further diluted with deionized water in a sample:deionized water ratio of 1:19. The total dilution ratio was 1:20,000.

The diluted samples prepared in i) and/or ii) were placed in a spectrophotometer (Perkin-Elmer Lambda 650 UV/VIS spectrophotometer) with a path length of 1 cm, and the UV and visible absorbance was measured. The extinction coefficient was calculated from the formula A = E c l, where A = absorbance, E = extinction coefficient in liters/grams/cm, c = concentration in grams/liter, and l = path length in cm.

The invention is illustrated by the following non-limiting examples.

Example 1
One mole of titanium oxydichloride in acidic solution was reacted with 3 moles of NaOH in aqueous solution. After an initial reaction period, the temperature was raised above 70°C and stirring was continued. The reaction mixture was neutralized by adding aqueous NaOH and allowed to cool below 70°C. After filtration, the resulting filter cake of precursor titanium dioxide particles was further dried to 20% by weight water using a rotary drier operating at 6 rpm. A screw conveyor was used to feed this material to a rotary calciner operating at 710°C with a residence time of 20 minutes. The treated titanium dioxide was ground to a fine powder using an IKA Werke dry powder mill operating at 3,250 rpm. The powder was reslurried in deionized water. To the resulting slurry was added an alkaline solution of sodium _aluminate equivalent to 3.5% by weight _Al2O3 relative to the _TiO2 weight, while maintaining the pH below 11. The temperature was maintained below 60°C during the addition. The temperature of the slurry was then increased to 75°C and 4.6% by weight sodium stearate relative to _TiO2 dissolved in hot water was added. The slurry was equilibrated for 45 minutes and neutralized by dropwise addition of 20% hydrochloric acid over 15 minutes, after which the slurry was allowed to cool to below 50°C. The slurry was filtered using a Buchner filter until the cake conductivity at 100 gdm ^-3 in water was less than 150 μS. The filter cake was oven dried at 110°C for 24 hours and ground to a fine powder by an IKA Werke dry powder mill operating at 3,250 rpm.

A dispersion was made by mixing 5.5 g of polyhydroxystearic acid with 39.5 g of C12-C15 alkyl benzoate and then adding 55 g of the dried calcined titanium dioxide powder made above to the mixture. The mixture was passed through a horizontal bead mill operating at 4,500 rpm containing zirconia beads as the grinding media for 60 minutes.

The precursor titanium dioxide particles, calcined titanium dioxide particles, coated titanium dioxide particles and dispersions thereof were subjected to the test procedures described in this disclosure and exhibited the following properties:

1) Precursor titanium dioxide particles:
BET specific surface area = 101 ^m2 g ^-1
Mercury porosimetry average pore size = 77.6 nm
Total pore area by mercury porosimetry at 59,950.54 psia = 72.6 m ² g ^-1
Average crystal size = 10 nm
Average length = 75 nm
Average width = 15 nm
Average aspect ratio = 5.0:1

2) Calcined titanium dioxide particles:
BET specific surface area = 31.9 ^m2 g ^-1
Mercury porosimetry average pore size = 119 nm
Mercury porosimetry total pore area at 59,950.54 psia = 36.7 m ² g ^-1
Average crystal size = 42.4 nm
Average length = 44 nm
Average width = 34 nm
Average aspect ratio = 1.3:1

3) Changes in the properties of titanium dioxide particles due to calcination:
Reduction in BET specific surface area = 68.4%
Mercury porosimetry mean pore size increase = 53.4%
Mercury Porosimetry Total Pore Area Reduction at 59,950.54 psia = 49.4%
Increase in average crystal size = 324%
Average width increase = 126.7%

4) Coated titanium dioxide particles:
BET specific surface area = 28.6 ^m2 g ^-1
Mercury porosimetry mean pore size = 107.9 nm
Mercury porosimetry total pore area at 59,950.54 psia = 37.9 m ² g ^-1

5) Titanium dioxide dispersion:
(a) Particle size by sedimentation;
i) D(v,0.5)=271 nm;
ii) D(n,0.5)=200 nm;

(b) Particle size by light scattering:
i) Z average = 148 nm
ii) Intensity average = 158 nm

(c) Extinction coefficient:

Example 2
An aqueous dispersion was made by mixing 6.2 g of polyglyceryl-2 caprate, 2.6 g of sucrose stearate, 2 g of jojoba oil, 0.6 g of squalane, 1 g of caprylyl caprylate, and 37.4 g of deionized water, and then adding 50 g of the titanium dioxide powder made in Example 1. The mixture was passed through a horizontal bead mill operating at 4,500 rpm containing zirconia beads as the grinding media for 60 minutes. The titanium dioxide dispersion was subjected to the test procedures described in this disclosure and exhibited the following properties:

Extinction coefficient:

Example 3
The titanium dioxide dispersion produced in Example 1 was used to prepare a sunscreen emulsion formulation having the following composition:

Procedure 1. Keltrol RD was dispersed in water and the remaining ingredients of Water Phase A were added to the mixture and heated to 65-80°C.
2. Oil Phase B ingredients were combined and heated to 75-80°C.
3. The oil phase was added to the water phase with stirring.
4. The mixture was homogenized for 1 minute.
5. The resulting emulsion was cooled to room temperature with stirring and Phase C preservatives were added below 40°C.

The sunscreen formulations were subjected to the testing procedures described in this disclosure and exhibited the following properties:
i) SPF=34
ii) UVA/UVB ratio = 0.684
iii) UVAPF=13
iv) Critical wavelength = 379 nm
v) ΔL=13.5
vi) ΔL/SPF ratio = 0.40

Example 4
One mole of titanium oxydichloride in acidic solution was reacted with 3 moles of NaOH in aqueous solution. After an initial reaction period, the temperature was raised to above 70°C and stirring was continued. The reaction mixture was neutralized by adding aqueous NaOH and allowed to cool below 70°C. After filtration, the resulting filter cake of precursor titanium dioxide particles was further dried to 5% by weight water using a fluidized bed (approximately 150°C for 2 hours). A screw conveyor was used to feed this material to a rotary calciner operating at 710°C with a residence time of 20 minutes. The treated titanium dioxide was ground to a fine powder using an IKA Werke dry powder mill operating at 3,250 rpm. The powder was reslurried in deionized water. To the resulting slurry was added an alkaline solution of sodium _aluminate equivalent to 3.5% by weight _Al2O3 relative to the _TiO2 weight, while maintaining the pH below 11. During the addition, the temperature was maintained below 60°C. The temperature of the slurry was then increased to 75°C and 4.6% by weight sodium stearate relative to _TiO2 dissolved in hot water was added. The slurry was equilibrated for 45 minutes and neutralized by dropwise addition of 20% hydrochloric acid over 15 minutes, after which the slurry was allowed to cool to below 50°C. The slurry was filtered using a Buchner filter until the conductivity of the cake at 100 gdm ^-3 in water was less than 150 μS. The filter cake was oven dried at 110°C for 24 hours and ground to a fine powder by an IKA Werke dry powder mill operating at 3,250 rpm.

A dispersion was made by mixing 5 g of polyhydroxystearic acid with 45 g of C12-C15 alkyl benzoate and then adding 50 g of the dried calcined titanium dioxide powder made above to the mixture. The mixture was passed through a horizontal bead mill operating at 4,500 rpm containing zirconia beads as the grinding media for 60 minutes.

The titanium dioxide dispersion was subjected to the test procedures described in this disclosure and exhibited the following properties:

(a) Particle size by sedimentation:
i) D(v,0.5)=196 nm
ii) D(n,0.5)=137 nm

(b) Particle size by light scattering:
i) Z average = 182 nm
ii) Intensity average = 203 nm

Extinction coefficient:

The above examples demonstrate the improved properties of titanium dioxide particles, methods of making same, titanium dioxide dispersions, and/or sunscreen products in accordance with the present invention.
Some of the embodiments of the invention related to the present invention are shown below.
[Aspect 1]
Titanium dioxide particles having a volume-based median particle size D(v,0.5) greater than 175 nm and an (E308 _x E360 ₎ /E524 _value greater than 300 l/g/cm.
[Aspect 2]
2. The titanium dioxide of embodiment 1, comprising: (i) a median particle size by numbers D(n,0.5) greater than 100 nm; and/or (ii) a Z-average particle size greater than 80 nm; and/or (iii) an intensity-average particle size greater than 90 nm.
[Aspect 3]
3. The titanium dioxide of claim 1 or 2, comprising an average aspect ratio of 1.05 to 1.55:1.
[Aspect 4]
Titanium dioxide particles comprising: (i) an average crystallite size of from 30.0 to 51.0 nm; and/or (ii) an average aspect ratio of from 1.05 to 1.55:1.
[Aspect 5]
5. The titanium dioxide of embodiment 4, comprising an average width of 22.0 to 46.0 nm.
[Aspect 6]
A titanium dioxide according to any one of the preceding aspects, comprising (i) an average crystallite size of from 30.0 to 51.0 nm, and/or (ii) an average width of from 22.0 to 46.0 nm.
[Aspect 7]
7. The titanium dioxide of any one of the preceding embodiments, comprising an (E ₃₀₈ ×E ₃₆₀ )/E ₅₂₄ value of 320 l/g/cm or greater .
[Aspect 8]
8. The titanium dioxide of any one of the preceding embodiments, comprising an average crystallite size of 37.0 to 47.0 nm.
[Aspect 9]
A titanium dioxide according to any one of the preceding aspects, comprising a BET specific surface area of 15 to 43 m ² g ⁻¹ .
[Aspect 10]
10. The titanium dioxide of any one of the preceding embodiments, comprising : (i) a mercury porosimetry total pore area at 59,950.54 psia of 22 to 55 m ² g ⁻¹ ; and/or (ii) a mercury porosimetry average pore diameter of 65 to 150 nm.
[Aspect 11]
11. The titanium dioxide of any one of the preceding embodiments, comprising an E ₃₀₈ ×E ₃₆₀ value greater than 1800 (l/g/cm) ² and less than 3500 (l/g/cm) ² .
[Aspect 12]
Titanium dioxide particles comprising: (i) an (E308 _x E360 ₎ / _E524 value of 320 l/g/cm or more, and optionally (ii) an E524 of 7.5 l/g/cm or less _, and/or an _E308 x E360 _value of greater than 2100 (l/g/cm) ² .
[Aspect 13]
13. The titanium dioxide of any one of the preceding embodiments, comprising an (E ₃₀₈ ×E ₃₆₀ )/E ₅₂₄ value equal to or greater than 320 l/g/cm and less than 650 l/g/cm .
[Aspect 14]
_14. The titanium dioxide of any one of the preceding claims, comprising at least one selected from the group consisting of: (i) an E of 5.2 to 7.5 l/g/cm _{; (} ii) an E of ³² to 50 l /g/cm; (iii) an E greater than 45 l/g/cm; and (iv) an E ×E value greater than ₁₈₀₀ (l/g/cm) ² and less than or equal to ₃₃₀₀ (l/g/cm )2.
[Aspect 15]
The titanium dioxide according to claim 14, comprising at least two selected from the group consisting of (i), (ii), (iii) and (iv).
[Aspect 16]
The titanium dioxide of claim 15, comprising all of (i), (ii), (iii), and (iv).
[Aspect 17]
A dispersion comprising a dispersing medium and titanium dioxide particles as defined in any one of embodiments 1 to 16.
[Aspect 18]
A sunscreen product comprising titanium dioxide particles as defined in any one of aspects 1 to 16 and/or a dispersion as defined in aspect 17.
[Aspect 19]
1. A method of producing titanium dioxide particles, comprising: (i) forming precursor titanium dioxide particles having an average aspect ratio of 3.0 to 7.0:1; (ii) calcining the precursor particles to produce calcined titanium dioxide particles having an average crystallite size of 30.0 to 51.0 nm and/or an average aspect ratio of 1.05 to 1.55:1; and optionally (iii) applying an inorganic and/or organic coating to the calcined titanium dioxide particles.
[Aspect 20]
20. The method of claim 19, wherein (i) the calcined particles have an average aspect ratio of 1.15 to 1.45:1; and/or (ii) the calcined particles have an average crystallite size of 37.0 to 47.0 nm.
[Aspect 21]
21. The method of claim 19 or 20, wherein the calcined titanium dioxide particles comprise (i) an E524 of 7.5 l/g/cm or less _, and/or (ii) an _E308 x E360 _value of greater than 1800 (l/g/cm) ² .
[Aspect 22]
_22. The method of any one of claims 19 to 21, wherein the calcined titanium dioxide particles comprise at least one selected from the group consisting of: (i) an E524 of 4.7 to 7.5 l/g/cm _, (ii) an _E360 of 32 to 50 l/g/cm ^, (iii) an E308 of greater than 45 l/g/cm , and (iv) an _E308 x _E360 value of greater than 1800 and less than or equal to 3300 (l/g/cm)2.
[Aspect 23]
23. The method of any one of claims 19 to 22, wherein upon calcination (i) the average width of the titanium dioxide particles increases by 60 to 200%, and/or (ii) the BET specific surface area decreases by 35 to 95%, and/or (iii) the average crystallite size increases by 200 to 400%.
[Aspect 24]
1. A process for heating precursor titanium dioxide particles at a temperature in excess of 400° C. to produce calcined titanium dioxide particles, wherein (i) the average width of the titanium dioxide particles increases by 60-200%, and/or (ii) the BET specific surface area decreases by 35-95%, and/or (iii) the average crystallite size increases by 200-400%.
[Aspect 25]
1. Titanium dioxide particles obtainable by a process comprising: (i) forming precursor titanium dioxide particles having an average aspect ratio of 3.0 to 7.0:1; (ii) calcining said precursor particles to produce calcined titanium dioxide particles; and optionally (iii) applying an inorganic and/or organic coating to said calcined titanium dioxide particles, said titanium dioxide particles having an E524 of 7.5 l/g/cm or less _and an ( _E308 x E360 ₎ / _E524 value of 320 l/g/cm or more .
[Aspect 26]
2. Use of calcination to improve the ultraviolet absorption properties of titanium dioxide particles, wherein the calcined particles have an (E308 _x E360 ₎ / _E524 value of 320 l/g/cm or greater.
[Aspect 27]
27. The use according to claim ₂₆ , wherein the calcined particles comprise at least one selected from the group consisting of: (i) an E524 of 4.7 to 7.5 l/g/cm _, (ii) an _E360 of greater than 27 l/g/cm, (iii) an E308 of greater than 45 l/g/cm , and (iv) an _E308 x _E360 value of greater than 1800 ( l/g/cm) ² .
[Aspect 28]
28. Use according to aspect 26 or 27, wherein the baking is carried out in a rotary baker.

Claims (20)

1. Titanium dioxide particles comprising a volume based median particle diameter D(v,0.5) greater than 175 nm, an (E x E)/E value _greater than ₃₀₀ l/g/cm, an E _x E value greater than ₁₈₀₀ (l/g/cm) ² and less than 3500 (l/g/cm) ² , an E greater than ₄₅ l _/ g/cm and less than or equal to 76 l/g/cm, _an E greater than 20 l/g/cm and less than or equal to 50 l/g/cm, an E from _4.7 to 7.5 l/g/cm, an average aspect ratio of 1.05 to 1.55:1, and an average crystallite size of 30.0 to 51.0 nm. Titanium dioxide particles according to claim 1, comprising: (i) a median particle size by number D(n,0.5) greater than 100 nm; and/or (ii) a Z-average particle size greater than 80 nm; and/or (iii) an intensity-average particle size greater than 90 nm. Titanium dioxide particles according to claim 1 or 2, having an average width of 22.0 to 46.0 nm. 4. Titanium dioxide particles according to any one of claims 1 to 3, comprising an ( _E308 x _E360 )/ _E524 value of 320 l/g/cm or greater. Titanium dioxide particles according to any one of claims 1 to 4, having an average crystal size of 37.0 to 47.0 nm. 6. Titanium dioxide particles according to claim 1, having a BET specific surface area of 15 to 43 m ² g ⁻¹ . 7. Titanium dioxide particles according to any one of claims 1 to 6, comprising (i) a mercury porosimetry total pore area at 59,950.54 psia of 22 to 55 m ² g ^-1 , and/or (ii) a mercury porosimetry average pore diameter of 65 to 150 nm. 8. Titanium dioxide particles according to any one of the preceding claims, comprising an ( _E308 x _E360 )/ _E524 value of 320 l/g/cm or more and less than 650 l/g/cm. 9. The titanium dioxide particles according to ^{any one of claims 1 to 8} , comprising at least one selected from the group consisting of: (i) an _E524 of 5.2 to 7.5 l/g/cm; (ii) an _E360 of 32 to 50 l/g/cm; and (iii) an _E308 × _E360 value of greater than 1800 (l/g/cm)2 and not greater than 3300 (l/g/cm) ² . Titanium dioxide particles according to claim 9, comprising at least two selected from the group consisting of (i), (ii), and (iii). Titanium dioxide particles according to claim 10, comprising all of (i), (ii), and (iii). A dispersion comprising a dispersion medium and titanium dioxide particles as defined in any one of claims 1 to 11. A sunscreen product comprising titanium dioxide particles as defined in any one of claims 1 to 11 and/or a dispersion as defined in claim 12. 12. A method for producing titanium dioxide particles as claimed in any one of claims 1 to 11, comprising: (i) forming precursor titanium dioxide particles having an average aspect ratio of from 3.0 to 7.0:1; (ii) calcining the precursor particles at a temperature greater than 400°C to produce a volume based median particle size D(v,0.5) greater than 175 nm; an ( _E308 x _E360 )/ _E524 value greater than 300 l/g/cm; an _E308 x _E360 value greater than 1800 (l/g/cm) ² and less than 3500 (l/g/cm) ² ; E308 greater than 45 l/g/cm and less than or equal to 76 l/g/cm; _E360 greater than 20 l/g/cm _and less than or equal to 50 l/g/cm _; , producing calcined titanium dioxide particles having an average crystal size of 30.0 to 51.0 nm and an average aspect ratio of 1.05 to 1.55:1, and optionally (iii) applying an inorganic and/or organic coating to said calcined titanium dioxide particles. The method of claim 14, wherein (i) the calcined particles have an average aspect ratio of 1.15 to 1.45:1, and/or (ii) the calcined particles have an average crystallite size of 37.0 to 47.0 nm. 16. The method of claim 14 or 15, wherein the calcined titanium dioxide particles comprise at least one selected from the group consisting of: (i) an _E360 of 32 to 50 l/g/cm, and (ii) an _E308 x _E360 value of greater than 1800 and less than or equal to 3300 (l/g/cm) ² . The method of any one of claims 14 to 16, wherein calcination (i) increases the average width of the titanium dioxide particles by 60 to 200%, and/or (ii) reduces the BET specific surface area by 35 to 95%, and/or (iii) increases the average crystal size by 200 to 400%. 2. Use of calcination at temperatures greater than 400°C to improve the ultraviolet absorption properties of titanium dioxide particles, wherein the calcined particles have a volume based median particle size D(v,0.5) greater than 175 nm, an ( _E308 x _E360 )/ _E524 value equal to or greater than 300 l/g/cm , an _E308 x E360 _value greater than 1800 (l/g/cm) ² and less than 3500 (l/g/cm) ² , an _E308 greater than 45 l/g/cm and less than or equal to 76 l/g/cm, an _E360 greater than 20 l/g/cm and less than or equal to 50 l/g/cm , an _E524 of 4.7 to 7.5 l/g/cm , an average aspect ratio of 1.05 to 1.55:1, and an average crystallite size of 30.0 to 51.0 nm . 20. The use of claim 18, wherein the calcined particles have an _E360 of greater than 27 l/g/cm and less than or equal to 50 l/g/cm. The use according to claim 18 or 19, wherein the baking is carried out in a rotary oven.